Increasingly, metals and inorganic semiconductors are being replaced in the electronics industry by electrically conductive organic polymers also known as ICP's (inherently conductive polymers). A new electrically conductive polymer system was developed by NASA's Kennedy Space Center and is described in U.S. Pat. Nos. 5,968,417 and 6,059,999 to Viswanathan. The polymer is an electrically conductive composition of linearly conjugated π-electron systems and residues of a sulfonated lignin or sulfonated polyflavonoid. The new system has increased water solubility, increased processibility and is highly crosslinkable. Of particular interest is lignosulfonic acid doped polyaniline. Lignosulfates are byproducts of the paper making industry and are environmentally safe and inexpensive. The lignosulfonic acid improves the solubility of the conjugated π-system, polyaniline.
Viswanathan developed these polymer systems for antistatic coatings to be applied on fibers and fabrics. The antistatic coating is useful for garments worn in clean rooms to prevent sparking and igniting in a combustible atmosphere.
Another use of lignosulfonic acid doped polyaniline is for corrosion control. Under the brand name of Ligno-PANI™, GeoTech Chemical Company (Akon, Ohio) has developed a coating additive of the inherently conductive polymer. Together with metal particles, Ligno-PANI™ is part of a coating system that GeoTech markets under the brand name CATIZE™. The CATIZE™ system is employed to inhibit corrosion on architectural structures such as steel bridges by slowing the growth of rust.
There are a number of potential uses for ICP's in self-supporting films. ICP's would have enormous value if they could be uniformly distributed into a plastic matrix and processed into films or sheeting for possible uses in the field of electrodissipative packaging, in laminate structures that protect work surfaces used in precision manufacture of semiconductor chips, or in wall paper in clean rooms and similar environments.
Of special interest would be the incorporation of ICP's into fluoropolymer films. Fluoropolymers, in spite of their relatively high cost, are widely used in electrical applications. Among their advantages are their resistance to chemical attack, especially oxidation, their high melting points, and their retention of useful properties over a very wide range of temperatures. Carbon filled fluoropolymer compositions for static-electric discharge applications are known and preferred to other conductive polymer systems when chemically active environments are to be encountered due to their relative inertness and solvent resistance. Carbon black is typically for the form of carbon used in these compositions
However, there are difficulties in manufacturing self-supporting films of fluorpolymer when carbon black is added to achieve conductivity. One difficulty is the relatively large and rapid rise in effective melt viscosity of the blend that occurs as the carbon black is added to the fluoropolymer. This large and rapid viscosity increase results in more difficult and time consuming processing. In addition, streaking or skipping can occur during film manufacturing and it is difficult to provide bactch-to-batch uniformity. At lower levels of carbon black where there is less influence on effective melt viscosity, the electrical conductivity can be lost entirely or may be in a range below that desired.
A self-supporting, conductive polymer film that provides a suitable level of conductivity, that can be manufactured easily with consistent uniformity would be highly desirable.